(a) Technical Field
The present disclosure relates to a fuel cell system. More particularly, the present invention relates to a hydrogen exhaust system for a fuel cell vehicle, which exhausts hydrogen suitably discharged from an anode of a fuel cell stack.
(b) Background
A fuel cell system applied to a hydrogen fuel cell vehicle as an environmental friendly vehicle preferably comprises a fuel cell stack for suitably generating electricity by an electrochemical reaction of reactant gases, a hydrogen supply system (“fuel processing system”) for suitably supplying hydrogen as a fuel to the fuel cell stack, an air supply system (“air processing system”) for suitably supplying oxygen-containing air as an oxidant required for the electrochemical reaction in the fuel cell stack, a thermal management system for suitably removing reaction heat from the fuel cell stack to the outside of the fuel cell system, controlling operation temperature of the fuel cell stack, and performing water management function, and a system controller for suitably controlling the overall operation of the fuel cell system.
According to certain preferred embodiments, the hydrogen supply system preferably includes a hydrogen tank, high-pressure and low-pressure regulators, a hydrogen supply valve, an ejector, and a hydrogen recirculation system, the air supply system includes an air blower and a humidifier, and the thermal management system preferably includes an electric water pump (coolant pump), a water tank, and a radiator.
Preferably, in the hydrogen supply system, high-pressure hydrogen that is supplied from the hydrogen tank sequentially passes through the high-pressure and low-pressure regulators, and the pressure-reduced hydrogen is then supplied to the fuel cell stack. Preferably, in the hydrogen recirculation system, a hydrogen recirculation blower is suitably provided at an anode (“fuel electrode” or “hydrogen electrode”) outlet of the fuel cell stack to recirculate unreacted hydrogen of the anode that is remaining after reaction to the anode, thereby recycling the hydrogen.
Preferably, nitrogen in the air supplied to a cathode (“air electrode” or “oxygen electrode”) of the fuel cell stack and product water produced in the cathode during the operation of the fuel cell stack migrate to the anode through an electrolyte membrane (crossover phenomenon).
Accordingly, the nitrogen reduces the partial pressure of hydrogen to suitably degrade the performance of the fuel cell stack, and the product water clogs flow fields to impede the migration of hydrogen. Accordingly, it is necessary to ensure stable operation of the fuel cell stack by periodically purging the anode.
Therefore, in a typical fuel cell system, a hydrogen purge valve is suitably provided in a hydrogen exhaust line at the anode outlet of the fuel cell stack to suitably discharge foreign substances such as nitrogen and water that have accumulated in the anode.
Preferably, during the above-described purging process, the hydrogen purge valve (e.g., solenoid valve) that is suitably installed in the hydrogen exhaust line is periodically opened and closed in the form of on/off pulses such that the nitrogen and water that are accumulated in the anode are suitably discharged to the hydrogen exhaust line. Preferably, the hydrogen present in the anode is suitably discharged together with the nitrogen and water.
Preferably, the hydrogen discharged during the anode purge may cause a problem. When the concentration of hydrogen discharged from the anode is high, there is a risk of explosion.
Accordingly, to prevent the risk of explosion due to the hydrogen exhaust, it is necessary to suitably minimize or dilute the concentration of hydrogen discharged from the anode within the range of explosion. Conventionally, a diluter is suitably installed in the hydrogen exhaust line to suitably dilute the hydrogen with ambient air.
In certain examples where the diluter is used, the hydrogen is only mixed with air and discharged, but the absolute amount of hydrogen is not suitably reduced. Accordingly, when the fuel cell system is while the vehicle is stopped or travels at a low speed at a place where many vehicles are parked such as an indoor parking lot which is not well ventilated, the hydrogen discharged from the vehicle may be accumulated around the vehicle, which may increase the possibility of explosion.
Further, it may be necessary to additionally provide a pipeline or an air supply system for introducing air into the diluter, which results in an increase in the cost and the complexity of the pipeline.
Furthermore, a post-treatment system for treating the hydrogen discharged from the fuel cell stack may be used. Accordingly, a catalyst combustion type post-treatment system or a flame combustion type post-treatment system may preferably be used. However, these post-treatment systems introduce a large amount of air into a reactor to burn the hydrogen discharged from the fuel cell stack, and thus there are problems that the pipeline is suitably complicated, the load of the air blower is suitably increased, and a separate air supply system is suitably required.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.